This invention relates generally to compressors, and more specifically to blades and vanes used in compression systems. As used herein, the term “fluid” includes gases and liquids.
In a gas turbine engine, air is pressurized in a compression module during operation. The air channeled through the compression module is mixed with fuel in a combustor and ignited, generating hot combustion gases which flow through turbine stages that extract energy therefrom for powering the fan and compressor rotors and generate engine thrust to propel an aircraft in flight or to power a load, such as an electrical generator.
The compressor includes a rotor assembly and a stator assembly. The rotor assembly includes a plurality of rotor blades extending radially outward from a disk. More specifically, each rotor blade extends radially between a platform adjacent the disk, to a tip. A gas flowpath through the rotor assembly is bound radially inward by the rotor blade platforms, and radially outward by a plurality of shrouds.
The stator assembly includes a plurality of circumferentially spaced apart stator vanes or airfoils that direct the compressed gas entering the compressor to the rotor blades. The stator vanes extend radially between an inner band and an outer band. A gas flowpath through the stator assembly is bound radially inward by the inner bands, and radially outward by outer bands. The vanes are typically made in arcuate segments with arcuate outer and inner band segments each having one or more vane airfoils per segment. The segments are conventionally joined together to collectively form a complete 360 Degree stator vane stage. The stator vane segements are mounted within a compressor casing. A vane stage comprises a plurality of circumferentially arranged vane segments, with each segment having a plurality of vane airfoils extending between an arcuate inner band and an arcuate outer band.
In some designs, the vane segments are supported solely at its outer band since a conventional annular seal member is disposed between rotor stages, preventing stationary support of the inner band as well. Accordingly, the vane airfoils in these vane segments are cantilevered from the outer band support which creates bending moments due to the fluid flowing between the vanes which must be suitably reacted or accommodated through the outer band. The bending moments in some of these airfoils may be significant since they are supported solely at their outer band, with the inner band thereof being unsupported.
During engine operation, the gas flow through the flow path induces mechanical, thermal, and aerodynamic loads on the airfoils. Some of these loads are transmitted by the airfoils to support structures in the engine through the outer bands that are coupled to the airfoil and reacted by the support structures. In some designs, the inner bands may also, similarly, transmit some of the loads applied on the airfoils by the gas flow and reacted by other support structures. Within at least some conventional gas turbine engines, the stresses in the airfoil near the interface with outer band and near the support structures may become large enough to cause distress in the airfoil. Under sufficiently large stresses, cracking may occur in the airfoils within the vane sector near support structure locations that react the loading applied to the vane airfoils in the vane sector by the gas flow. Designing with additional thickness at these high locations may not be possible for several reasons, such as, aerodynamic considerations, flow modifications, additional weight and changed dynamic characteristics of the vanes and/or excessive leakages in the vane sectors.
Accordingly, it is would be desirable to have an airfoil assembly having features that reduce the stresses in the airfoil near the interface with the bands that support the airfoil while minimizing leakages in the vane sector. It would be desirable to have a method of manufacturing an airfoil assembly having features that reduce the stresses in the airfoil and having an interface with the bands that support the airfoil.